1. Field of the Invention
The present invention generally relates to a manufacturing method of a semiconductor device and a semiconductor device and, more particularly, to a manufacturing method of a semiconductor device and a semiconductor device which device has a redistribution layer.
Recently, as a semiconductor device has been rapidly miniaturized and given a higher density, mounting terminals thereof have accordingly been narrowly pitched. Especially for a CSP (Chip Size Package), the above-mentioned narrow pitch makes a serious problem when the CSP has mounting terminals provided on electrode pads formed on the periphery of a semiconductor element, because the semiconductor element has substantially the same size as the package itself.
Due to this, mounting terminals and electrode pads are formed in an offset state so that the mounting terminals are formed in a matrix in a package. This structure requires wirings (hereinafter referred to as redistribution layers) to connect the mounting terminals and the electrode pads.
On the other hand, a semiconductor device is required to be manufactured at a low cost. Accordingly, the above-mentioned redistribution layers need to be formed at a low cost.
2. Description of the Related Art
Recently, wafer-level techniques have been applied in manufacturing a CSP-type semiconductor device, in which techniques redistribution layers are formed before dicing (separating into pieces) a wafer.
In a conventional method of forming a redistribution layer on a wafer, a resist is first formed on a wafer except on an electrode pad and a region on which the redistribution layer is to be formed. Then, a metal film is formed as a redistribution layer by sputtering or electroplating. In this process, copper (Cu) is used as a material of the redistribution layer because of good electric conduction. Additionally, a surface plating of nickel (Ni) or gold (Au) is provided on the metal film, if necessary.
After the metal film is formed, the resist is removed so as to complete forming the redistribution layer that is electrically connected to the electrode pad on the wafer. After the redistribution layer is formed, steps including a step of forming a sealing resin and a step of providing a mounting terminal are performed. Thereafter, the wafer is diced into each semiconductor device.
As described above, a conventional method of manufacturing a semiconductor device employs a sputtering method or an electroplating method to form a redistribution layer. However, using a sputtering method requires expensive manufacturing facilities so as to raise a product cost of the semiconductor device.
In using an electroplating method, a base metal film needs to be preparatorily formed as an electrode connected to a power source at a position at which the redistribution layer is to be formed, which complicates the manufacturing steps. Further, in using the electroplating method, since a metal film is deposited slowly, forming a thick redistribution layer requires a long time so as to reduce a manufacturing efficiency thereof.
It is a general object of the present invention to provide an improved and useful manufacturing method of a semiconductor device and a semiconductor device in which method and device the above-mentioned problems are eliminated.
A more specific object of the present invention is to provide a manufacturing method of a semiconductor device and a semiconductor device which device can be manufactured efficiently at a low cost.
In order to achieve the above-mentioned objects, there is provided according to one aspect of the present invention a method of manufacturing a semiconductor device, the method comprising:
a wire-forming step of forming a wiring (redistribution layer) on a substrate having an electrode pad so as to connect the electrode pad to a mounting terminal,
wherein the wire-forming step includes the steps of:
applying a metal foil to the substrate by providing an adhesive therebetween;
patterning the metal foil into a predetermined pattern so as to form the wiring; and
connecting the wiring to the electrode pad electrically.
According to the present invention, since the wiring connecting an electrode pad and a mounting terminal is composed of a metal foil, the wiring can be formed at a reduced cost. In other words, if the wiring is formed by electroplating or sputtering, this requires expensive manufacturing facilities so as to raise a cost of the semiconductor device manufactured by these manufacturing facilities. In addition, forming the wiring (redistribution layer) by electroplating or sputtering requires a long time so as to reduce a manufacturing efficiency thereof.
To the contrary, since techniques to manufacture the metal foil are already established, as well as techniques to apply the metal foil by using an adhesive, the wire-forming step can be performed efficiently and at a low cost.
Additionally, in the semiconductor device manufacturing method according to the present invention, the adhesive may be an elastic adhesive.
According to the present invention, since the adhesive is elastic, the adhesive can undergo an elastic deformation so as to absorb irregularities on the upper surface of the substrate. Therefore, the metal foil is guaranteed to be flat and uniform when applied thereon.
Additionally, in the semiconductor device manufacturing method according to the present invention, the step of connecting may be performed after the step of applying, and the step of applying may include removing a portion of the metal foil positioned above the electrode pad and a portion of the adhesive applied on the electrode pad.
According to the present invention, in connecting the electrode pad and the metal foil after applying the metal foil on the substrate by using the adhesive, portions of the metal foil and the adhesive opposing the electrode pad are removed therefrom. Therefore, the electrode pad and the metal foil can easily be connected electrically.
Additionally, in the semiconductor device manufacturing method according to the present invention, the step of applying may include removing the portion of the metal foil positioned above the electrode pad and the portion of the adhesive applied on the electrode pad by etching.
According to the present invention, the metal foil and the adhesive on the electrode pad can be removed by spraying an etching solution or by soaking in an etching solution. This makes the removing step simple and efficient. Additionally, the removing process by etching is more precise than a removing process by machining, and costs less than a removing process by micromachining such as an ion beam machining.
Additionally, in the semiconductor device manufacturing method according to the present invention, a step of forming a barrier metal layer on the electrode pad may be performed before the step of applying.
According to the present invention, the barrier metal layer covers the electrode pad. In removing the metal foil and the adhesive by etching, the electrode pad has a risk of being damaged by an etching solution. However, forming the barrier metal layer on the electrode pad as above prevents the etching solution from damaging the electrode pad.
Additionally, in the semiconductor device manufacturing method according to the present invention, the step of applying may include removing the portion of the metal foil positioned above the electrode pad and the portion of the adhesive applied on the electrode pad by a laser.
According to the present invention, the laser can precisely remove the portions of the metal foil and the adhesive in a short time.
Additionally, in the semiconductor device manufacturing method according to the present invention, the step of connecting may include forming a metal film by electroless plating so that the metal film connects the wiring to the electrode pad electrically.
According to the present invention, the wiring can be formed at a reduced cost because electroless plating requires manufacturing facilities of a lower cost than electroplating and sputtering. Additionally, in the electroless plating, the metal film electrically connecting the metal foil and the electrode pad can be formed simply by soaking the substrate after the step of removing the portions of the metal foil and the adhesive on the electrode pad. Therefore, the metal foil and the electrode pad can be electrically connected easily with few steps. Further, in the electroless plating, since the metal film is formed also on the adhesive exposed at the inner wall of the removed portion, the metal foil and the electrode pad can surely be connected electrically.
Additionally, in the semiconductor device manufacturing method according to the present invention, the step of connecting may include forming the metal film by electroless plating so that the metal film connects the wiring to the electrode pad electrically, and that the metal film is formed on the metal foil patterned in the step of patterning.
According to the present invention, forming the metal film on the patterned metal foil (the wiring) prevents a migration from occurring between the adjacent wirings.
Additionally, in the semiconductor device manufacturing method according to the present invention, the metal foil may be made of copper (Cu).
According to the present invention, the metal foil (the wiring) can have good electric properties because copper (Cu) has a smaller impedance. On the other hand, copper (Cu) is a substance likely to cause a migration. However, forming the metal film on the patterned copper foil (the wiring) prevents a migration from occurring between the adjacent wirings, as mentioned above, so that a signal transmission speed can be increased, and the semiconductor device can be more reliable.
Additionally, in the semiconductor device manufacturing method according to the present invention, a step of forming a connection electrode on the electrode pad may be performed before the step of applying so that the step of connecting includes a step of joining the metal foil to the connection electrode by heating so as to connect the metal foil and the connection electrode electrically.
According to the present invention, the step of removing the portions of the metal foil and the adhesive opposing the electrode pad is not required, and the electrode pad and the metal foil can be electrically connected simply by heating. This facilitates the wire-forming step.
Additionally, in the semiconductor device manufacturing method according to the present invention, a step of forming the mounting terminal on the metal foil may be performed after the step of applying.
According to the present invention, since the mounting terminal is formed as a part of the metal foil, a step of independently forming a mounting terminal is unnecessary. Therefore, with the shortened manufacturing steps, the semiconductor device can be manufactured more efficiently.
In order to achieve the above-mentioned objects, there is also provided according to another aspect of the present invention a semiconductor device comprising:
a semiconductor element having an electrode pad;
a mounting terminal to be connected to a mounting substrate; and
a wiring electrically connecting the electrode pad to the mounting terminal, at least a part of the wiring being formed of a metal foil.
According to the present invention, a metal foil forms at least a part of a wiring electrically connecting an electrode pad and a mounting terminal. Since such a metal foil can be formed easily at a low cost, this directly leads to decreasing the cost of the semiconductor device.
Additionally, in the semiconductor device according to the present invention, the metal foil may be applied to the semiconductor element via an elastic adhesive applied on the semiconductor element.
According to the present invention, in mounting the semiconductor device on the mounting substrate, even though the mounting substrate and the semiconductor element undergo different amounts of thermal expansion, the adhesive can absorb stresses originating from the different amounts of thermal expansion. This prevents the mounting terminal from being damaged or separated, and thus makes the semiconductor device more reliable in mounting.
Additionally, in the semiconductor device according to the present invention, the mounting terminal may be formed as a unitary part of the metal foil.
According to the present invention, the mounting terminal and the wiring can be formed at the same time. Therefore, the semiconductor device can be manufactured more simply.
Additionally, in the semiconductor device according to the present invention, the metal foil may be a copper (Cu) foil.
According to the present invention, the metal foil (the wiring) can have good electric properties because copper (Cu) has a smaller impedance. On the other hand, copper (Cu) is a substance likely to cause a migration. However, forming the copper foil as only a part of the wiring keeps a migration from occurring between the adjacent wirings, so that a signal transmission speed can be increased, and the semiconductor device can be more reliable.
Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read conjunction with the accompanying drawings.